Maintaining or improving the ride quality of elevators will require implementation of new technologies, especially as the elevator speeds are increased. Reducing lateral motion of the car platform is important for improving ride quality. Such motion can be caused by rail-induced forces which are transmitted to the car through the rail guides due to rail irregularities.
If one were to design an automatic control system for reducing such lateral motion one could choose an open loop system.
At least one attempt to address rail-induced forces using an open loop control is shown in the literature. In U.S. Pat. No. 4,750,590, in order to compensate for lateral oscillation of an elevator car, Matti Otala discloses what appears to be an open-loop elevator control system with solenoid actuated guide shoes. The disclosure purports to show how to use the concept of first ascertaining the out-of-straightness of the guide rails for storage in a computer memory and subsequently controlling the guide shoes by recalling the corresponding information from memory and correcting the guide rail shoe positions accordingly.
However, the method shown in Otala's disclosure, of merely attaching acceleration meters to the elevator car, would not, as suggested by his disclosure, provide sufficient information to create a "deviation table" for a compensation system. It would merely create an acceleration table. How a "deviation table" is made from acceleration meters; is not shown or suggested.
There are two principal disturbances which contribute to the levels of vibration in the car: (1) rail-induced forces which are transmitted to the car through the rail guides due to rail irregularities, and (2) direct-car forces such as produced by wind buffeting, passenger load, distribution or motion.
The various parameters of the elevator car's suspension system are so affected by unrepeatable direct-car forces that the underlying acceleration measurements, without more, would not be meaningful. In other words, the underlying accelerations are a nonlinear function of the car load, its distribution, the movement of passengers, and a myriad of other direct car forces. Something more is needed to interpret the sensed acceleration signals (or deviations integrated therefrom) in a meaningful context in order to be enabled to compile a displacement table that truly reflects the rail profile.